1. Field of the Invention
The present invention relates to a member used in a display apparatus and a display apparatus using the member and, more particularly, to a member that is used as a back panel or a spacer of a display apparatus.
2. Description of Related Art
Display apparatuses such as plasma display panel (PDP), plasma arrayed liquid crystal display (PALC) and field emission display (FED) have been used as high resolution display apparatuses that emit light by stimulating a fluorescent bodies with electron beams or ultraviolet rays in a gas or vacuum.
The field emission display (hereinafter referred to as FED), for example, comprises a back panel 1 provided with an electron source, and a front panel 2 that is disposed to oppose the back panel 1 via spacer 3 and a side wall 4 as shown in FIG. 1, wherein the electron source that functions as a cathode 1a is provided on the back panel 1 and an anode such as fluorescent bodies 2a is provided on the front panel 2, so that electron beam emitted by the cathode hits the fluorescent bodies, thus causing the fluorescent bodies to emit light so as to form a picture.
The back panel 1 and the spacer 3 of the FED are formed from glass by applying the technique to form a glass-made vacuum tube used in a cathode ray tube display (hereinafter referred to as CRT) or the substrate of a liquid crystal display (hereinafter abbreviated to LCD) that function by a principle of light emission similar to that of the FED.
As a material to make the back panel 1 and the spacer 3, Japanese Unexamined Patent Publication (Kokai) No. 2001-261365 discloses a glass for substrates comprising 10 to 50 mol % of Al2O3, 20 to 70 mol % of CaO, 25 mol % or less of SiO2, MgO, SrO, BaO, ZnO, TiO2, Y2O3 and La2O3, and 15 mol % or less of ZrO2, Li2O, Na2O and K2O. This glass has a Young's modulus in a range from 83 to 124 GPa, a specific rigidity in a range from 33.4×109 to 38.6×109 cm and a linear expansion coefficient in a range from 8.4×10−6 to 9.7×10−6/°C. in a temperature range from 50 to 350° C.
Japanese Unexamined Patent Publication (Kokai) No. 2001-184624 discloses one having higher mechanical strength and comprising glass ceramic that contains lithium disilicide (Li2O-2SiO2) as the principal crystal phase and contains 4 to 8% by weight of Li2O on oxide basis, a material showing Young's modulus in a range from 95 to 120 GPa, a specific rigidity in a range from 39.4×109 to 47.1×109 cm and a linear expansion coefficient in a range from 6.5×10−6 to 13.0×10−6/° C. in a temperature range from −50 to 70° C.
Japanese Unexamined Patent Publication (Kokai) No. 2000-95559 discloses a composite glass ceramic material having higher Young's modulus and higher thermal conductivity with composition of 40 to 95% by weight of glass ceramic comprising 50 to 62% by weight of SiO2, 5 to 10% by weight of P2O5, 22 to 26% by weight of Al2O3, 3 to 5% by weight of Li2O, 0.6 to 2% by weight of MgO, 0.5 to 2% by weight of ZnO, 0.3 to 4% by weight of CaO, 0.5 to 4% by weight of BaO, 1 to 4% by weight of TiO2, 1 to 4% by weight of ZrO2 and 0 to 2% by weight of As2O3, and including a solid solution of β-quartz as crystal phase, and 5 to 60% by weight of filler that contains carbide, the material showing a Young's modulus in a range from 122 to 195 GPa, a linear expansion coefficient in a range from 0.3 to 5.0×10−6/° C. in a temperature range from 50 to 360° C. and a heat conductivity in a range from 2.8 to 11.6 W/m·K.
Recently there have been increasing demands for thinner and larger displays. The display member disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2001-261365 has a somewhat high Young's modulus, but has a low specific rigidity in a range from 33.4×109 to 38.6×109 cm. The member disclosed in Japanese Unexamined Patent Publication (Kokai) No. 2001-184624 has a low value of Young's modulus in a range from 95 to 120 GPa, that may cause deflection due to gravity or external force when used as the back panel 1 or the spacer 3.
That is, there is such a problem that, when bonding the back panel 1, the front panel 2, the spacer 3 and the side wall 4 together, the inner space of the display must be pumped to generate vacuum of 0.133×10−3 Pa or higher, upon which the member may not withstand the atmospheric pressure.
The FED, on the other hand, uses a plurality of electron sources as small as 1 μm or less to cause a single pixel to illuminate. As a result, the display apparatus as a whole uses a significantly large number of electron sources that become heat sources when thermal electron emission is employed similarly to the CRT wherein filaments are heated to emit electrons, thus making it difficult to cool the apparatus.
To avoid the problem described above, an electron source (called the cold cathode) that employs field electron emission is used instead of thermal electron emission. Even in this case, there has been such a problem that thermal spots may be generated depending on the position in the apparatus resulting in deterioration of picture quality, since glass has very low heat conductivity of 3 W/m·K or less.
Moreover, while the FED requires a higher surface accuracy of the back panel 1 whereon the cathodes are mounted to serve as the electron sources, high accuracy of processing cannot be achieved because the conventional glass has a low Young's modulus.
The ceramic material disclosed in Japanese Pant Unexamined Publication No. 2000-95559 has a high Young's modulus but has a low linear expansion coefficient in a range from 0.3 to 5.0×10−6/° C. that leads to such a problem that leakage may be caused resulting in lower vacuum inside of the apparatus due to crack caused in a joint when bonding the members, or low accuracy of the apparatus due to deflection, both resulting in lower picture quality.
Moreover, the back panel 1 and the spacer 3 are required to be made of a material that is not a complete insulator but has a certain level of electrical conductivity, since the spacer 3 may be charged and the FED may become unable to function when the volume resistivity is too high. However, in the prior art, glass made to have electrical conductivity tends to experience a decrease in Young's modulus, a decrease in specific rigidity and a decrease in heat conductivity and/or variation in the coefficient of linear expansion depending on the concentrations of the additive components.